Artificial lift method for low pressure sagd wells

ABSTRACT

A pumping system includes a hydraulic motor assembly configured to drive a production pump. The hydraulic motor assembly includes a master pump located on the surface and an electric motor configured to controllably power the master pump. When moved by the electric motor, the master pump discharges a working fluid under pressure. The pressurized working fluid is transferred to a hydraulic turbine located in the wellbore. The hydraulic turbine converts the pressure of the working fluid into torque, which is transferred through a driveline to a production pump. The production pump pressurizes production fluids, which are carried under pressure to the surface.

FIELD OF THE INVENTION

This invention relates generally to the field of submersible pumping systems, and more particularly, but not by way of limitation, to a hydraulically-driven submersible pumping system configured for use in high-temperatures applications.

BACKGROUND

Submersible pumping systems are often deployed into wells to recover petroleum fluids from subterranean reservoirs. Historically, submersible pumping systems have included one or more fluid filled electric motors coupled to one or more high performance pumps located above the motor. When energized, the electric motor provides torque to the pump, which pushes wellbore fluids to the surface through production tubing. Each of the components in a submersible pumping system must be engineered to withstand the inhospitable downhole environment.

Although widely accepted, the conductors and insulators within the electric motors may be inadequate for certain high-temperature downhole applications. In particular, motors employed in downhole applications where modern steam-assisted gravity drainage (SAGD) recovery methods are employed are be subjected to elevated temperatures. Electrical insulation materials often fail under these elevated temperatures or under prolonged exposure to wellbore fluids and contaminants. If an electrical insulator is compromised by these conditions, an electrical short may occur that causes the complete failure of the electric motor. There is, therefore, a need for a downhole pumping system that exhibits enhanced resistance to heat, corrosive chemicals, mechanical wear and other aggravating factors experienced in modern SAGD wells. It is to this and other deficiencies in the prior art that the present invention is directed.

SUMMARY OF THE INVENTION

In a preferred embodiment, a pumping system includes a hydraulic motor assembly configured to drive a production pump. The hydraulic motor assembly includes a master pump located on the surface and an electric motor configured to controllably power the master pump. When moved by the electric motor, the master pump discharges a working fluid under pressure. The pressurized working fluid is transferred to a hydraulic turbine located in the wellbore. The hydraulic turbine converts the pressure of the working fluid into torque, which is transferred through a driveline to a production pump. The production pump pressurizes production fluids, which are carried under pressure to the surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a submersible pumping system constructed in accordance with a preferred embodiment of the present invention.

FIG. 2 is a partial cross-sectional view of the production pump of the submersible pumping system of FIG. 1.

FIG. 3 is a partial cross-sectional view of the hydraulic turbine of the submersible pumping system of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In accordance with a preferred embodiment of the present invention, FIG. 1 shows an elevational view of a pumping system 100. The pumping system 100 generally includes a hydraulic motor assembly 102, a production pump 104 and production tubing 106. The pumping system 100 is generally configured to pump fluids through the production tubing 106 from a subterranean wellbore 108 to a wellhead 110 located on the surface. The wellbore 108 is drilled for the production of a fluid such as water or petroleum. As used herein, the term “petroleum” refers broadly to all mineral hydrocarbons, such as crude oil, gas and combinations of oil and gas.

Unlike convention submersible pumping systems, the pumping system 100 does not include an electric motor within the wellbore 108. In place of the conventional electrical motor, the production pump 104 is driven by the hydraulic motor assembly 102. The hydraulic motor assembly 102 includes a master pump 112, an electric motor 114 and a hydraulic turbine 116. The master pump 112 and electric motor 114 are preferably located on the surface. The electric motor 114 is connected to, and drives, the master pump 112.

The master pump 112 is connected to the hydraulic turbine 116 through a feed line 118 and a return line 120. The feed line 118 extends from the surface, through the wellbore 108 to the hydraulic turbine 116. The working fluid is returned to the surface from the hydraulic turbine 116 through the return line 120. In preferred embodiments, the hydraulic motor assembly 102 further includes a surface-mounted reservoir 122 that receives working fluid from the return line 120 and a dedicated suction line 124 extending from the reservoir 122 to the master pump 112. The reservoir 122 provides a buffer and accumulator for the working fluid to ensure that the master pump 112 is provided with a constant, uninterrupted supply of working fluid. It will be appreciated that the feed line 118, return line 120 and production tubing 106 each preferably routed through the wellhead 110 so that the internal pressure of the wellbore 108 can be safely contained.

The hydraulic turbine 116 is located in the wellbore 108 and is operably connected to the production pump 104 through a series of connected shafts (not shown in FIG. 1) to enable the transfer of torque and rotation from the hydraulic turbine 116 to the production pump 104. The pumping system 100 preferably includes a seal section 126 and a thrust section 128 disposed between the hydraulic turbine 116 and the production pump 104. It will be appreciated that the seal section 126 and thrust section 128 each include intermediate shafts that transfer torque from the hydraulic turbine 116 to the production pump 104.

During operation, the electric motor 114 is selectively energized with a motor controller. The electric motor 114 then transfers torque through a shaft or coupling to the master pump 112. The master pump 112 pressurizes a working fluid that is discharged from the master pump 112 through the feed line 118. The feed line 118 provides the pressurized working fluid to the hydraulic turbine 116. The hydraulic turbine rotates in response to the application of pressurized working fluid and thereby converts a portion of the energy stored as working fluid pressure into torque.

The hydraulic turbine 116 transfers the torque to the production pump 104 through a driveline 130. The driveline 130 preferably includes a series of connected shafts 132 that extend from the hydraulic turbine 116, through the seal section 126, the thrust section 128 and into the production pump 104. The seal section 126 isolates the hydraulic turbine 116 from the production fluids and contaminants found in the wellbore 108 and production pump 104. The seal section 126 preferably includes a series of mechanical seals, bellows or seal bags to prevent the contamination of the clean working fluid found in the hydraulic turbine 116. The thrust section 128 includes a series of thrust bearings that oppose the axial movement of the driveline 130. Reducing the axial movement of the driveline 130 reduces wear on the internal components connected to the shafts 132.

Once driven by the hydraulic turbine 116, the production pump 104 pushes production fluids from the wellbore 108 to the surface through the production tubing 106. The working fluid is returned from the hydraulic turbine 116 under lower pressure to the reservoir 122, before being drawn back into the master pump 112. The speed and other operational characteristics of the production pump 104 can be adjusted by controlling the output of the master pump 112. In this way, the production pump 104 can be driven without the placement of an electrical motor in the wellbore 104. In high-temperatures applications, the ability to remove sensitive electrical components from the wellbore 108 presents a significant advancement in the art.

Turning to FIG. 2, shown therein is a partial cross-sectional view of the production pump 104. The production pump 104 preferably includes a production pump housing 134, a plurality of production pump stages 136, a production pump intake 138 and a production pump discharge 140.

Each production pump stage 136 includes a production pump diffuser 142 and a production pump impeller 144. The production pump impellers 144 are each connected for rotation with the shaft 132. As the production pump impellers 114 rotate, they impart kinetic energy into the production fluid. A portion of the kinetic energy is then converted into pressure as the production fluid passes through the corresponding production pump diffuser 144. It will be appreciated that production fluid is drawn into the production pump 104 through the production pump intake 138 and discharged under higher pressure through the production pump discharge 140. Although the production pump 104 has been disclosed in preferred embodiments as a turbomachine, it will be appreciated that the production pump 104 could alternatively be configured as a positive displacement pump that incorporates screws or spiraled flights to impart motion to the production fluid.

Turning to FIG. 3, shown therein is a partial cross-sectional view of a preferred embodiment of the hydraulic turbine 116. The hydraulic turbine 116 is preferably configured as a conventional turbomachine turned upside-down. In this configuration, the hydraulic turbine 116 converts a portion of the energy from the pressurized working fluid into torque. The torque is then transferred through the driveline 130 into the production pump 104.

The hydraulic turbine 116 preferably includes a turbine housing 146, one or more turbine stages 148, a turbine intake 150 and a turbine discharge 152. Pressurized working fluid is introduced to the hydraulic turbine 116 from the feed line 118 through the turbine intake 150. As noted in FIG. 3, the turbine diffusers 156 and turbine impellers 154 are provided in a “reverse orientation” to the “standard orientation” of the production pump diffusers 144 and production pump impellers 142. As pressurized working fluid is forced through the hydraulic turbine 116, the turbine impellers 154 rotate in response to the pressurized fluid. The pressurized fluid exits from the hydraulic turbine 116 into the return line through the turbine discharge 152.

In a presently preferred embodiment, the hydraulic turbine 116 and production pump 104 are sized and configured to produce offsetting thrust forces. The hydraulic turbine produces an upward thrust along the driveline 130, while the production pump 104 produces a downward thrust. In a particularly preferred embodiment, the production pump 104, the hydraulic turbine 116 and the master pump 112 are collectively configured to minimize the amount of differential thrust transferred across the driveline 130. By limiting the amount of differential thrust, the size of the thrust section 128 can be reduced.

In a particularly preferred embodiment, portions of the pumping system 100 are preassembled before being introduced into the well. For example, the thrust section 128 can be oil serviced before connection to the seal section 126 and production pump 104. The feed line 118 and return line 120 can be connected to the hydraulic turbine 116 before deployment. In an alternate preferred embodiment, the feed line 118 and return line 120 can be ganged or collected together within a single housing. In yet another preferred embodiment, the feed line 118, return line 120 and production tubing 106 are located within a common housing.

It is to be understood that even though numerous characteristics and advantages of various embodiments of the present invention have been set forth in the foregoing description, together with details of the structure and functions of various embodiments of the invention, this disclosure is illustrative only, and changes may be made in detail, especially in matters of structure and arrangement of parts within the principles of the present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. It will be appreciated by those skilled in the art that the teachings of the present invention can be applied to other systems without departing from the scope and spirit of the present invention. 

What is claimed is:
 1. A pumping system that includes components located on the surface and components located in the wellbore, the pumping system comprising: a hydraulic motor assembly; wherein the hydraulic motor assembly comprises: a motor located on the surface; a master pump connected to the electric motor, wherein the master pump discharges a working fluid under pressure; and a hydraulic turbine located in the wellbore and driven by the pressurized working fluid discharged from the master pump; a production pump positioned within the wellbore; and a driveline that connects the hydraulic turbine to the production pump.
 2. The pumping system of claim 1, further comprising: a seal section connected to the hydraulic turbine; and a thrust section connected between the seal section and the production pump.
 3. The pumping system of claim 1, wherein the hydraulic turbine comprises: one or more turbine diffusers; one or more turbine impellers; a turbine intake; and a turbine discharge.
 4. The pumping system of claim 3, wherein the feed line is connected to the turbine intake.
 5. The pumping system of claim 4, wherein the hydraulic motor assembly further comprises a return line connected to the turbine discharge.
 6. The pumping system of claim 3, wherein the production pump comprises: a production pump intake; a production pump discharge; one or more production pump impellers; and one or more production pump diffusers.
 7. The pumping system of claim 6, wherein each of the one or more turbine impellers has an orientation that is opposite to the orientation of each of the one or more production pump impellers.
 8. The pumping system of claim 6, wherein each of the one or more turbine diffusers has an orientation that is opposite to the orientation of each of the one or more production pump diffusers.
 9. The pumping system of claim 1, wherein the hydraulic motor assembly further comprises: a reservoir connected to the return line; and a suction line connected between the reservoir and the master pump.
 10. A pumping system configured to transfer production fluids from a subterranean wellbore to surface facilities, the pumping system comprising: a production pump, wherein the production pump comprises: an intake that receives the production fluids; and a discharge; production tubing connected to the discharge of the production pump; and a hydraulic motor assembly configured to drive the production pump, wherein the hydraulic motor assembly does not include an electric motor located within the wellbore.
 11. The pumping system of claim 10, wherein the hydraulic motor assembly comprises: a master pump located on the surface; and a motor connected to the master pump.
 12. The pumping system of claim 11, wherein the hydraulic motor assembly further comprises a hydraulic turbine positioned within the wellbore.
 13. The pumping system of claim 12, wherein the production pump is a positive displacement type pump.
 14. The pumping system of claim 12, wherein the production pump is a turbomachine that includes a plurality of production pump impellers that are configured in a standard orientation.
 15. The pumping system of claim 14, wherein the hydraulic turbine includes a plurality of turbine impellers that are configured in a reverse orientation.
 16. A method for moving production fluids from a subterranean wellbore to surface facilities, the method comprising the steps of: pressurizing a working fluid with a master pump; transferring the pressurized working fluid to a hydraulic turbine positioned in the wellbore; generating torque by passing the pressurized working fluid through the hydraulic turbine; transferring the torque from the hydraulic turbine to a production pump; drawing the production fluids into the production pump through a production pump intake; and discharging the production fluids from the production pump through production tubing.
 17. The method of claim 16, further comprising the step of returning the working fluid from the hydraulic turbine to the master pump.
 18. The method of claim 16, further comprising the steps of: operating the hydraulic turbine at a first speed to generate a hydraulic turbine thrust; and operating the production pump at the first speed to generate a production pump thrust that substantially offsets the hydraulic turbine thrust. 